"All houses as well as a market and a health centre were completely looted and the market burnt. Over 100 women were raped, six in front of their fathers who were later killed," he said.

A further 150 women and 200 children were abducted.

This attack a fortnight ago is one of many across the arid territory.

Village after village is being razed to the ground by the militias, he said.

To compound the problem, aid agencies can only reach small parts of Darfur and are subject to attacks.

Mr Kapila called for more aid and for urgent international intervention to bring about a ceasefire in the war.

Shock

"I was present in Rwanda at the time of the genocide, and I've seen many other situations around the world and I am totally shocked at what is going on in Darfur," he told the BBC Radio 4's Today programme.

"This is ethnic cleansing, this is the world's greatest humanitarian crisis, and I don't know why the world isn't doing more about it."

The fighting in the west of Sudan has intensified as government peace talks to resolve the 20-year war with southern rebels are nearing an end.

But the UN is concerned that this conflict could undermine the peace talks in Kenya.